The present invention relates to apparatus for melting hollow metal ingots during electroslag remelting of consumable electrodes and may be used in melting pipes of round, square, rectangular and the like cross-sectional shapes.
At present it is known to use for melting hollow metal ingots by electroslag remelting of consumable electrodes an apparatus comprising a hollow chilled mould, a mandrel introduced into the internal space of the chilled mould to define the cavity of the ingot being melted, and a bottom plate comprising a chilled plate. The hollow chilled mould is mounted with its end face on the flat surface of the bottom plate prior to the beginning of the ingot melting cycle so that the bottom plate serves as a bottom wall of the mould.
It should be, however, noted that during the melting of a hollow metal ingot involving the relative displacement of the ingot and the chilled mould at the beginning of the melting cycle where the hollow chilled mould is on the bottom plate, the mandrel is jammed with the solidifying metal of the hollow ingot. This is due to the fact that the first portions of molten metal are intensively solidified upon hitting against the cold bottom plate so that they jam the mandrel as a result of shrinkage.
In order to prevent the mandrel from being jammed with the ingot during the shrinkage thereof, the mandrel or the bottom plate is displaced relative to the chilled mould.
However, in view of the difficulties encountered in selecting a desired speed of movement of the hollow chilled mould, the bottom plate or the mandrel, it is not possible to eliminate the jamming of the mandrel with the hollow ingot being moulded in all cases. At low speeds of movement of the hollow mould or the mandrel, the jamming of the mandrel with the ingot being moulded may occur, whereas at high speeds thereof molten metal may penetrate through the space between the lower end face of the chilled mould and the bottom plate.
As a result of experiments and studies, the inventors have come to the conclusion that it is highly desirable to start the melting process for obtaining a hollow metal ingot with the hollow chilled mould and the mandrel in a fixed position relative to the bottom plate or at a very low speed of their relative movement. In this case a reliable cohesion between the hollow ingot being moulded and the bottom plate is ensured, and the solidification of molten metal which thus occurs complies with requirements imposed in conformity with the production technique for ingot melting, while the penetration of molten metal through the space between the lower end face of the chilled mould and the bottom plate is completely eliminated. The jamming of the mandrel with the hollow ingot being moulded represents, however, an important problem associated so far with the process of melting hollow ingots.